Coprecipitation occurs from supersaturated calcium car-Sorption of europium(III) on calcite from aqueous solution was bonate solutions. In undersaturated solutions, interactions investigated by kinetics and sorption isotherms at 323 K and by with the surface of minerals through sorption and desorption site-selective and time-resolved luminescence spectroscopy at 15 phenomena may occur. Sorption is indeed an important fac-K. Three sorption sites (A, B, C) were characterized by this last tor in the migration of toxic or radioactive elements in surtechnique. B constitutes a major family which appears in all samface or underground waters. Sorption is also a preliminary ples with sorbed Eu and is characterized by an environment involvstep in coprecipitation. ing water or hydroxyl ions. The C family is observed only for the The necessity of acquiring reliable data on sorption has highest Eu concentrations. In these sites, the environment is more increased in connection with the projects for disposal of hydrated than in sites B. Site A constitutes a minority but appears in all samples. It corresponds to the centrosymmetric structural long-lived radioactive wastes in geological repositories (9). Ca site of calcite in position 2b, thus demonstrating that sorbed The idea is that the surrounding rocks will act as a natural Eu(III) can substitute for Ca in calcite. ᭧ 1997 Academic Press barrier against the spread of radioactivity into the biosphere Key Words: sorption; europium(III); neodymium(III); calcite; after the corrosion of the canisters and dissolution of the site-selective and time-resolved luminescence spectroscopy. packing materials. It is important to evaluate the long-term safety of such barriers by estimating the role of sorption phenomena on the retardation of the migration of radionu-1 To whom correspondence should be addressed.
probes. Among the trivalent rare earth elements, Eu 3/ is the 440